Pronunciation of a consonant letter is determined by its position in a word. For example, the letter called so so is pronounced [s] at the start of a syllable, but [t] at the end. Only [p], [t], [k] and the nasals [n], [m], [ŋ] can occur syllable-finally, with the result that each of these sounds can be represented by a number of letters in the syllable-final position. One letter represents different sounds in different contexts. The prescribed pronunciation is [r], but in colloquial speech it is often pronounced [l]. The pronunciation of this letter can be a useful sociolinguistic indicator.
Consonants are divided into three classes. There are five tones in the Thai language; tone is indicated by a combination of consonant class, the degree to which the syllable is open or closed, vowel length, and whether or not the syllable bears one of four tone markers. A chart to illustrate the tone marking system can be found at thaitranslate.com. There is some flexibility in the pronunciation of tones; in informal speech, tones are not always pronounced as they are traditionally written, however in formal speech or recitations pronunciation follows the written form.
Consonant letters cannot be conjoined to form ligatures, but a virama symbol called pinthu is used to mute the inherent vowel and enable consonant clusters to be written.
Consonants are ordered according to place of articulation, roughly with those articulated furthest back in the oral cavity coming first and those articulated furthest forward coming near the end. Sibilants and liquids are ordered at the end.